A slip ring is a device which enables two members, which rotate relative to each other, to stay in electrical communication. For example, a small telescope may have a base which includes a stationary portion and a movable portion which rotates relative to the base. A slip ring installed between the stationary portion and the movable portion provides continuous electrical connectivity between these portions (e.g., to control a telescope motor, to convey optical or radio signals captured by the telescope, etc.).
If a cable were used in place of the slip ring, it would be possible for the cable to become awkwardly wound around the telescope and/or for the cable to become severely twisted around itself. Considerable manual effort would be required to prevent the cable from tangling and/or interfering with access around the telescope.
Conventional slip rings come in a variety of standard sizes. When designing an apparatus which uses a slip ring, a designer typically identifies a general size of the moving parts of the apparatus. Next, the designer selects a particular standard sized slip ring, and configures the precise dimensions of the moving parts of the apparatus to that standard sized slip ring.